Post on 30-Jan-2016
description
transcript
Exploding stars
László Kiss, School of Physics, University of Sydney
1572: Tycho Brahediscovered a newstar in Cassiopeia...
“De nova stella...”
(“About a new star...”)
...which faded away after a year. Today a hot gas cloud is visible there (mostly in X-rays).
(Chandra)
See also: ancient “guest stars” in Chinese, Korean and Japanese chronicles
AD 1006
AD 1054
AD 185
AD 1181
The zoo of close binary stars
Cataclysmic variable stars: interacting semidetached binaries with an accretion disk
(Keele University)
Three types of “novae”
dwarf novaeaccretion disk instability, no thermonuclear reactions, repetitive process (5-5,000 days)
classical novaethermonuclear runaway on the white dwarf's surface, repetitive process (10-10,000 years)
(Type Ia) supernovaeirreversible destruction of the white dwarf
(Chandra PR)
Dwarf novae: no real explosion
(U Gem, J. Blackwell)
Accretion disk instability...
...driven by the hydrogenionization at 10,000 K
The light curve of RX And (1974-2000)
Classical novae: “new” stars never noticed before
outburst amplitude: 7-12 mag (V1500 Cyg: >20 mag!)
rapid fading after maximum (speed classes using tn)
absolute magnitudes in maximum: -7 ... -10 mag
MV ~ an+bn log tn
(n=2, 3)
Discovery: a task for amateur astronomers
(APOD)
Like Nova Cygni 2001/2 (V2275 Cyg)...
“A spectrum is worth thousand light curves...”
E.g.: the existence of an accretion disk in dwarf novae
Confirmation: by spectroscopy
dwarf nova in outburst?H lines in absorption (thick accrection disk)
new nova?H, He, Fe, ... lines in emission (ejected gas cloud)
new (Ia) supernova?no hydrogen lines, few broad features
A spectrum tells the difference
Expansion kinematics: the P Cygni profile
(Carroll & Ostlie 1996)
V5115 Sgr (Nova Sgr 2005)
Late spectra: geometry of the shell
(Gill & O'Brien, 1999, MNRAS, 307, 677)
Like V1494 Aql (Nova Aql 1999/2), 5 years later:
Novae and distances: expansion parallax
GK Per(Nova Per 1901)
First approximation:d=vexp (t-t0)/
Supernovae: stars that can outshine a whole galaxy!
(HST)
(SNe 1999el and 2000E)
Types of supernovae (simplified)
The nearest and brightest since 1604: SN 1987A in the Large Magellanic Cloud
“Light echoes”: lightscattered by interstellardust clouds
System geometry
(P. Garnavich)
“The Lord of the Rings”: gas rings around SN 1987A, ejected by the progenitor
(HST)
Types of supernovae (simplified)
The expansion of the Universe is accelerating!
Brian SchmidtANU, Canberra
Even bigger explosions:
Hypernovae: very massive Type II SNe, thought to produce 100x more energy than “regular” SNe
Gamma Ray Bursts (GRBs): rapid flashes across the electromagnetic spectrum. Massive stars collapsing to black holes (related to hypernovae); binary mergers (e.g. two neutron stars collapsing into a black hole)
...and the story goes on